Magnetic materials



Nov. 11, 1947. B GOULD 2,430,464

MAGNETIC MATERIALS Filed July 8, 1942.

DIRECTION OF THE MADNE TIC FIELDS [t APPL/E D BEFORE AND DURING THE BAKEMAGNET/C SHOCK IN OERSTEDS APPL/ED AND REMOVED BEFORE EACH DETERMINATIONOF H. L. B. GOULD BY WWW/W A T TOR/VET? Patented Nov. 11, 1947 MAGNETICMATERIALS Harold L. B. Gould, Towaco, N. J assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication July 8, 1942, Serial No. 450,170

Claims. 1

The invention relates to improvements in magnetic materials and moreparticularly to improvements in alloys which have a cobalt content ofbetween about to percent, a nickel content of about 45 percent and aremaining content essentially of iron.

An object of the invention is to provide a method of treating the saidalloys to stabilize their magnetic properties so that they remainsubstantially unchanged after the application and removal of amagnetizing force.

Another object is to provide magnetic material of the said type withstabilized magnetic properties.

Another object is to provide magnetic circuits for electromagneticcommunication apparatus, which will have substantially stable magneticproperties, so that the apparatus may retain its operatingcharacteristics substantially unchanged after being subjectedtemporarily to normal or accidental magnetization.

Cobalt-nickel-iron alloys to which the invention may be applied for theattainment of the stated objects have been described in United StatesPatents 1,715,541 and 1,715,647 issued to G. W. Elmen on June 4, 1928.

These alloys when properly treated have highly desirable magneticproperties for certain purposes, such as for use in communicationapparatus operated at voice or carrier frequencies, for example,continuously loaded conductors, loading coils and transformers. Thesealloys are particularly suited for those purposes on account of theirconstant permeability and their almost negligible hysteresis loss.

It has, however, been observed that some of the magnetic properties ofthese alloys produced in accordance with prior art methods are sensitiveto temporary magnetizing forces applied accidentally or in the course ofnormal operation. Thus it has been found that after such magnetizationthe initial permeability has changed and that the change depends uponthe intensity of the previously applied magnetic field, beingparticularly great within a comparatively low range of magnetizingforces.

The initial permeability o referred to in this specification and in theappended claims is that generally known as the reversible permeabilityand is the permeability of a sample measured at small alternating fluxdensities superimposed on the residual flux due to a previousmagnetization.

A treatment of said alloys for the purpose of stabilizing their magneticproperties has been described in the United States Patent 1,848,364issued to V. E. Legg on March 8, 1932. In accordance with Leggsdisclosure a ring sample of the 2 alloy is first "annealed in the usualmanner and is then magnetized in a given direction at high fieldstrength (50 oersteds) after removal of this field the sample is bakedat a suitable temperature (between 400 and 600 C.) for a considerabletime (36 to 48 hours).

Legg found that by his treatment the initial permeability was markedlystabilized under certain conditions. Thus after the application of amagnetic shock in a given direction to the annealed and baked sample theinitial permeability would remain practically unaffected by anysubsequent, magnetization in the same direction but would changeconsiderably after a shock applied in a direction opposite that of thefirst shock. This instability was found to be considerably beyond thelimits usually considered acceptable for communication apparatus of thetype referred to above.

It is therefore a more specific object of the invention to produce amagnetic alloy of the said type having an initial permeability whichwill not vary more than about 2 to 5 per cent after temporarymagnetization over a wide range of magnetizing forcesapplied in eitheror both directions.

It is still another specific object to produce a cobalt-nickel-ironalloy with such stabilized magnetic properties without excessivelyincreasing the hysteresis losses.

In accordance with a principal feature of the invention a body of thecobalt-nickel-iron alloy is first annealed, then subjected to a strongmagnetizing force in a given direction, then baked for several hourswith an appreciable unidirectional or alternating magnetizing forceapplied at least during a part of the baking period.

In the following description reference will be made to the accompanyingdrawing, in which:

Fig. 1 is a diagrammatic representation of a toroidal core C having awinding W thereon; and Fig. 2 is a graph or curve showing the variationin initial permeability of a typical sample, embodying the invention,due to application to the sample of magnetic fields of differentstrengths. For thepurposes of the investigation, samples 7 were preparedin the form of toroidal cores, such as are frequently used for loadingcoils. Such a core C is shown diagrammatically in Fig. 1. The cores werewound of a continuous ribbon of the magnetic alloy, 0.008 inch inthickness. Experience indicates that even better results may be obtainedwith samples made of compressed powder of the alloys in which theparticles are coated with an insulating film in well-known manner andfor well-known purposes.

The alloys of the samples were composed of different proportions ofcobalt, nickel and iron, as described more in detail below. Forinformation about the production of these alloys and their propertiesreference may be had to the Elmen patents already referred to.

Each sample was first annealed in hydrogen at a temperature well abovethe Curie point and the subsequent bake was at temperatures below theCurie point, substantially as disclosed by Legg in his patent alreadyreferred to.

1 detail.

Table I. C'O-45 Ni- Fe (Curie Point 685 C'.)

a b c d e f g M M lgerrg eability agnetizing aximum 0e icient X we tars?as? variation of Oersteds- 0, Per Cent High Low 425 15 D. 24 10 425 10D. 1 519 34 .05 425 v 3 D. 3 505 1 03 425 1 D. 24 418 3 06 455 3 D. 3515 8 02 465 10 D. 1 375 2 05 465 3 D. 3 501 l .02 465 3 D. 4. 5 509 4.5 .03 465 3 D. 6 372 4. 5 .07 465 2 D. 4 520 3 .09 .02 465 3 A. 3 476 3.20 .02 465 5.2 A. C 3 432 .6 13 .02 465 0 608 14 .80 .04 490 3 D. 3.5564 .5 .05 .02 510 3 D. 3 574 1.3 35 .05 540 3 D. 3 486 1. 2

Table II.25 C045 N130 Fe (Curze Pomt 725 C'.)

a b c d e j a M M lerniesbility Temperaagnetlzmg Duration of InitialPermea-mmum 0e Clem Core 0 Force, i Variation of ture, C. OerstedsField, Hrs. ability, 0 my Per Cent High Low 425 15 24 99 3 425 10 1 30840 465 10 l .5 465 3 D. 4. 5 230 1.1 465 3 D. 6 208 6 465 2 D. 4 288 16465 0. 322 18 510 3 D. 228 .6 540 3 D. 251 .4 540 0..- 378 15 Table III.23 C'O-45 Ni-32 Fe (Curie Point 715 C.)

Table IV.7 C'070 N1-23 Fe (Curie Point 640 C.)

a b c d e f 0 M t' M zl i i Temperaagne mug Duration of InitialPermea-xmlum 0e Clem Core Force, 1 Variation of ture, C. Oersteds Field,Hrs. ability, #0 My Per Cent High Low 1 (X P210 465 3D. 0 3 434 .7 .67.11 P209 465 0 720 14. 3 1. 3 19 In the tabulation given above, there islisted certain data for the bake and other data for the observed resultsof the bake for each of the samples Thus, column a of the tabulationgives the core numbers of the different samples which have previouslybeen annealed and subjected to a saturating field. Column b gives thetemperature of the bake in degrees centigrade. Column c gives themagnetizing forc in oersteds of the magnetic field applied during thebake in the same direction as the previously applied saturating field.Column 41 gives the duration of the field applied during the first partof the bake. Column e gives the initial permeability no based uponmeasurements taken immediately after the bake with a very smallalternating field. Column f gives the maximum variation in initialpermeability co in per cent of the permeability given in column 6 anddue to application of magnetic fields of varying strength applied afterthe bake, as will be explained below. Column 9 gives the high and lowvalues of the permeability coefiicient A, the values in the table to bemultiplied by 10- this coefficient is obtained from the same tests asthose in column f. As explained below, the permeability coefficient is ameasure of the hysteresis loss.

The Table I is for alloys of 20% Co, 45% Ni, 35% Fe, which have beenpreviously annealed at 850 C. for one hour in a hydrogen atmosphere.

The Table II is for alloys of 25% Co, 45% Ni, 30% Fe, which have beenpreviously annealed at 850 C. for one hour in a hydrogen atmosphere.

Table III is for alloys of 23% Co, 45% Ni, 32% Fe, which have beenpreviously annealed at 850 C. for one hour in a hydrogen atmosphere.

Table IV is for alloys of 7% Co, 70% Ni, 23% Fe, annealed at 1000 C. forone hour in a hydrogen atmosphere.

Each sample of the different alloys was subjected before the bake to asaturating field of 50 oersteds in a given direction. The bake for eachsample was maintained for 24 hours and during the initial part of thebake a magnetic field was applied in the same direction as the previoussaturating field. The fiux produced in the sample during the bakingtreatment was substantially greater than the residual flux due to thesaturating field applied before the bake. As exceptions, the samplesP101A and P103A in Table I were subjected to an alternating field of 60cycles per second.

The procedure for a typical sample will now be described. Thus referringto the core P119A in Table I, this core was first annealed at 850 C. forone hour in a hydrogen atmosphere. Upon cooling, the magnetizing windingwas wound upon the core and a magnetizing force of 50 oersteds wasmomentarily applied producing a high degree of saturation. The core withthe winding was then placed in the furnace and heated to 490 C. in ahydrogen atmosphere for 24 hours. During the first 3.5 hours of the bakea magnetizing force of 3 oersteds was applied to the core.

Upon cooling and before any appreciable magnetizing force had beenapplied to the core, tests were made at low alternating magnetizingforces to determine the initial permeability which was found to be 563.

Thereafter the core was momentarily magnetized with a suitable lowmagnetizing force in the same direction as that applied during the bakeand after removal of this field the initial permeability was againdetermined in the same manner as before. A series of similar tests werethen made with increasing fields up to 50 oersteds, all applied in thesame direction as the bake field, and after each field had been removedthe initial permeability Was determined. Thereafter a second series ofsimilar tests were made with the momentary field applied in the oppositedirection of the bake field beginning at low field intensity andincreasing up to a saturating field and after each application of thefield the initial permeability was again determined. The various valuesof the initial permeability obtained after momentary application of thecorresponding magnetizing forces are plotted in the curve shown in Fig.2 of the drawing where the ordinates represent the initial permeabilityno and the abscissae the magnetizing force in oersteds of themomentarily applied fields; the fields to the right in the curve were inthe same direction as the bake field and those in the left direction ofthe curve were in the opposite direction.

From the curve it will be noted that the original initial permeabilitywas 563 and that the initial permeability increased to 564 after theapplication of a very small field and retained this value after theapplication of fields up to 50 oersteds in the same direction as thebake flux. When the momentary field was reversed the initialpermeability remained at 564 up to 1 oersted, thereupon it suddenlydecreased to 562 at the point P and increased to 565, returning to 564at the higher fields applied in the opposite direction of the bakingfield. The total variation from 562 to 565 of the initial permeabilityis less than 1 per cent.

As is well known, the hysteresis losses may be expressed by thepermeability coefiicient 1 (in Ft a-B where [L is the permeability atsmall alternating fields and B is the change in fiuX density in thesample at the small alternating fields.

The tests for the permeability coefiicient of core P119A were made inconjunction with the tests for the initial permeability after eachremoval of the momentarily applied fields. It was found that the'coefiicient A was equal to .02 10- over the entire range, except for anarrow range around the point P where the initial permeability shows asharp peak; here the value of A was equal to .05 10- The curve shown inthe drawing for the sample core P1l9A is typical for all of the samplesin showing a comparatively uniform value for #0 over the entire range inboth directions and in showing a sudden variation in ,uo afterapplication of comparatively light fields in the direction opposite thelast heavy magnetization. The behavior of the permeability coeificientof the sample core P119A is also typical in the fact that the maximumvalue coincides in general with the peak variation in ,uo.

The procedure in testing the core Pll9A is somewhat simplified and wasadopted after a more complicated procedure had been tried in connectionwith several samples. Thus in accordance with the more complicatedprocedure the sample was baked and subjected to a field during the bakeas described above; after the bake, tests for ,uo and A were made afterapplication of each of a series of increasing fields up to a saturatingfield in the same direction as the bake field; then a series of testswas taken with decreasing fields in the same direction; then a thirdseries of tests was made with increasing fields up to a saturating fieldin the opposite direction of the bake field, and a fourth series withdecreasing fields in the opposite direction of the bake field; a fifthseries of tests was then made with increasing fields in the samedirection as the bake field and further series would repeat the tests inthe second, third and fourth series, as desired.

From these tests it was found that the permeability curve would show nopeak during the first and second series, would show a peak during thethird series but not timing the fourth series and would again show apeak during the fifth series but not during the sixth series. In otherwords, it may be concluded that the peaks occur in a given directionuntil the material has been magnetized beyond the range at which thepeak occurs and in the same direction. Thus after the bake the materialis still under the influence of the saturating field applied before thebake, for which reason there is no peak in the permeability curve duringthe first and second series of tests in the same direction as thesaturating field.

The procedure outlined for the core P119A was carried out in a similarmanner for all of the other cores listed in the tabulation. As willappear from the tables, in some cases an alternating field was appliedduring the bake instead of a unidirectional field and in other cases nofield was applied at all during the bake for the sake of comparison. Insome cases the bake was carried out with a field applied during theentire time of the bake.

A sample core P93, not listed in the tabulation, was specially treated;it was of the type which is listed in Table I. The baking temperaturewas 425 C. and a magnetizing force of .63 oersted was applied during theentire baking time of 14 hours and during the subsequent cooling. Theinitial permeability was 588 and the maximum variation in initialpermeability due to application of momentarily applied fields up to asaturating field was 3.4 per cent; i was .09 10- The same core wasthereupon baked at 425 C. for another 24 hours with a magnetic field of.63 oersted applied during the entire bake and during the subsequentcooling, giving an initial permeability of 510 and variation in theinitial permeability of 2 per cent over the same range as before; Avaried from .25 at the peak of no to .05 10- where Was normal. The samecore was then further baked at 425 with a field of .63 oersted appliedduring the baking period of 24 hours and during the subsequent cooling,giving an initial permeability of 477 with a variation in permeabilityof 2 per cent; i changed from .21 to .04

From the experiments described above it was found that th variations inpermeability were smaller when the baking field was applied in the samedirection as the saturating field applied before the bake, than when thebake field was in the opposite direction.

It was also found that a high baking field applied for a long timeduring the bake tends to -reduce materially the permeability of thealloy.

It was further found that the application of an appreciable field for along time during the bake tends to materially increase A and thereforethe hysteresis losses.

It appears from the data of the tabulation that low values for variationin #0 and for i will be secured by baking the alloys at temperaturesbetween 450 and 550 approximately and applying a field during the firstportion of the bake with a magnetizing force of about 3 oersteds forfrom 3 to 6 hours or of greater magnetizing force for a shorter time,as, for example, a magnetizing force of 10 oersteds for 1 hour. Withtreatments within the stated limits, variations in the initialpermeability will be limited to 5 per cent and i will remain less than.7 X 10**.

However, it is possible, as in the case of the core P119A in Table I,the cores P183 and P177 in Table II, the core P181 in Table III and thecore P210 in Table IV to secure an initial permeability which willremain stable within 1 per cent after any magnetic shock up tosaturation, and at the same time secure low hysteresis losses.

From the specific tests of the core P93 referred to above, it appearsthat similar results may be obtained with a small magnetizing forceapplied during the entire baking period; a being very high at this fieldstrength, the corresponding fiux is, of course, greater than theresidual fiux due to the saturating field applied before the bake.

In the claims reference is made to a directed magnetic field. This doesnot necessarily mean a field extending in a straight line through thebody of material but includes, by way of example, a field whichtraverses a toroid in a circular direction or a field which traverses anL-shaped member through the two arms of the L in series.

What is claimed is:

1. A body of a magnetic alloy containing between 20 and 25 per cent ofcobalt, 45 per cent of nickel and the balance essentially of iron andhaving been heated to between 425 and 540 C. for a period of severalhours after having been annealed in hydrogen and then temporarilymagnetized substantially to saturation by the application thereto of amagnetizing force, said body having been less strongly magnetized duringthe first few hours of said heating period to reduce variation in itsinitial permeability, caused by subsequent magnetization of anyintensity and direction, to not more than 5 per cent.

2. A body of a magnetic alloy containing about 20 to 25 per cent ofcobalt, 45 per cent of nickel and the balance essentially of iron andhaving been heated to between 425 and 540 C. for a period of twenty-fourhours after having been annealed in hydrogen and then temporarilymagnetized by the application thereto of a substantially saturatingmagnetic field, said body having been magnetized during the initialthree to six hours, approximately, of said heating period by theapplication thereto of a magnetizing force of about 3 oersteds toprevent more than 5 per cent variation in the initial permeability ofsaid alloy caused by subsequent magnetization of any intensity anddirection.

3. A body of a magnetic alloy containing about 20 to 25 per cent ofcobalt, 45 per cent of nickel and the balance essentially of iron andhaving been heated to between 425 and 540 C. for a period of twenty-fourhours after having been annealed in hydrogen and then temporarilymagnetized by the application thereto of a substantially saturatingmagnetic field, said body having been magnetized during the initialthree hours, approximately, of said heating period by the applicationthereto of a magnetizing force of about 3 oersteds.

4. A body of a magnetic alloy containing about 20 to 25 per cent ofcobalt, 45 per cent of nickel and the balance essentially of iron andhaving been heated to between 425 and 540 C. for a period of twenty-fourhours after having been annealed in a hydrogen atmosphere and thentemporarily magnetized by the application thereto of a substantiallysaturating magnetic field in a given direction, said body having beenmagnetized during the initial three hours, approximately, of saidheating period by the application thereto in said given direction of aunidirectional magnetizing force of about 3 oersteds.

5. A body of a magnetic alloy containing about 20 to 25 per cent ofcobalt, 45 per cent of nickel and the balance essentially of iron andhaving been heated to between 425 and 450 C. for a period of twenty-fourhours after having been annealed in hydrogen and then temporarilymagnetized by the application thereto of a substantially saturatingmagnetic field, said body having been magnetized during about the firsthour of said heating period by the application thereto of a magnetizingforce of about 10 oersteds.

6. A method of treating a body of magnetic material, which has a cobaltcontent of between about 20 to 25 per cent, a nickel content of about 45per cent and a remaining content essentially of iron and which has beenannealed in a hydrogen atmosphere, to insure that the permeabilitycoeilicient of said body will remain not more than .7 10 and that theinitial permeability of said body will vary not more than 5 per centwhen the body has been magnetized to any intensity and in any directionsubsequent to the treatment, said method comprising first temporarilymagnetizing the body by applying thereto a substantially saturatingmagnetic field, then heating the body to a temperature between about 425and 540 C. for a period of several hours and during at least a fractionof said heating period magnetizing said body less strongly,

7. A method of treating a hydrogen annealed body of magnetic materialthat has a magnetic property which before the treatment was unstablewithin a certain range of applied field intensities, said materialhaving a cobalt content of about 20 to 25 per cent, a nickel content of45 per cent and a remaining content essentially of iron, said methodcomprising first temporarily magnetizing said material by applyingthereto a substantially saturating magnetic field, then heating thematerial to a temperature between about 425 and 540 C. for a period ofseveral hours, and during a fraction of said heating period of aboutthree to six hours magnetizing the material by applying a magnetic fieldthereto of about 3 oersteds to substantially stabilize said propertywithin said range of field intensities applied in the given or theopposite direction.

8. A method of treating a body of magnetic material which has a cobaltcontent of between about 20 to 25 per cent, a nickel content of about 45per cent and a remaining content essentially of iron, said methodcomprising first annealing said material in hydrogen, then temporarilymagnetizing said material by applying thereto a substantially saturatingmagnetic field in a, given direction, then heating the material to atemperature between about 425 to 540 C. for a period of abouttwenty-four hours, and during a fraction of said heating period of aboutthree hours magnetizing the material by applying thereto in said givendirection a unidirectional magnetic field of about 3 oersteds.

9. A method of treating a body of magnetic material to reduce variationin one of its magnetic properties due to magnetization of any intensityand in any direction, said material having a cobalt content of 20 percent, a nickel content of 45 per cent and a remaining content ofessentially iron, said material having been annealed in hydrogen, saidmethod comprising first temporarily magnetizing said body by applyingthereto a substantially saturating magnetic field in a given direction,then heating the body to a temperature between about 425 and 540 C. fora period of about twenty-four hours and during the first three hoursapproximately of said heating period magnetizing the body by applyingthereto a similarly, including oppositely, directed magnetic field of 3oersteds.

10. A method of treating a body of magnetic material that has a magneticproperty which before the treatment was unstable within a certain rangeof applied field intensities, said material having a cobalt content ofabout 20 to 25 per cent, a nickel content of 45 per cent and a remainingcontent essentially of iron, said material having been annealed inhydrogen, said method comprising first temporarily magnetizing saidmaterial by applying thereto a substantially saturating magnetic field,then heating the material to a temperature between about 425 and 540 C.for a period of several hours, and during about the first hour ofsaidheating period magnetizing the body by applying a magnetic fieldthereto of about 10 oersteds to substantially stabilize said propertywithin said range of field intensities applied in the given or theopposite direction.

HAROLD L. B. GOULD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Electrical Engineering, Dec.1935, pages 1292 to 1299.

